1. Field
The present invention relates to a process to transfer a Time division Multiplexing (TDM) frame over a MPLS network, said frame comprising a plurality of time slots with specific bandwidths
2. Description of the Related Art
European and Asian network SDH (Network Node Interface for the Synchronous Digital Hierarchy; see International Telecommunication Union, recommendation G.707. March 1996) and its American homologue SONET (Synchronous Optical Network Transport Systems; see GR-253-CORE, issue 2, Revision A, December 1997) are inflexible TDM (Time Division Multiplexing) based transport architectures.
These optical networks have large bandwidth, good reliability and are mostly used in voice transport, that knows an increasingly success. SDH/SONET proposes a frame structure in which the different afferent signals are mixed or multiplexed by synchronised interlacing of octets and are encapsulated into virtual containers of a given size. A given number of containers hanged together are sent by time slots. The bandwidth (size, data rate) of the time slots depends on the hierarchy optical level of the SDH/SONET and on the transport structure of the optical fibre network (see ITU; standard G.803 Architectures of Transport networks based on the synchronous digital hierarchy).
The hierarchy level gives the line rate of the communication in the manner set forth in table 1 for SDH and SONET, wherein respectively STM (Synchronous Transport Module) and OC (Optical Container) are unitary data carrier.
TABLE 1OpticalOpticalLinelevel SDHlevel SONETRate (Mbps)OC-151STM-1OC-3155STM-4OC-12622STM-16OC-482500STM-64OC-19210000STM-128OC-38420000STM-256OC-76840000
The transport structure of SDH/SONET establishes the number of channels the SDH/SONET line rate uses for the transport.
The entire line rate can be transported on a “concatenated” (or “clear”) channel, which means that the entire line rate is available as a single channel of communication and that the entire line rate may be used by a single flow of time slots.
Otherwise the line rate can be “channelized” and the line rate is subdivided into multiple fixed rate channels. For example, the payload of an OC-48 link may be subdivided into four OC-12 channels. In this case, the data rate of a single time slot flow is limited by and to the bandwidth of an individual channel.
To summarise, SDH/SONET frames are transported in a synchronised manner, by a succession of predefined bandwidth time slots, the bandwidth of the time slot depending on the conditions of the SDH/SONET transmission.
MPLS (Multiprotocol Label Switching Architecture; see Internet Engineering Task Force, RFC 3031) networks are wire networks that provide a good handiness for the bandwidth administration and the development of the quality of service in terms of scaleability, routing and adaptability. In a MPLS network the data are transferred by packets on LSPs (Label Switched Paths) having specific bandwidths.
The transfer of SDH/SONET frames over a MPLS network is necessary when a SDH/SONET network goes through a MPLS network because there is no other path or because a network operator wants to control and monitor the information transmitted on the SDH/SONET network.
A process to transfer a SDH/SONET frame over a MPLS network exists and consists in cutting the SDH/SONET frame or more precisely each associated time slots when they enter the MPLS network in order to create packets with given bandwidths that can go through the pre-existing LSPs of the MPLS network. The cut is done according to the bandwidth of the existing LSPs. The time slots and thus the SDH/SONET frame are then reconstructed (reassembled) at the output of the MPLS network by rearranging all the packets ones after the others. The cut and the reconstruction of the SDH/SONET frame occur respectively into input and output routers of the MPLS network.
This process does not ensure an optimal transfer of the SDH/SONET frames because the time slots have to be cut and the reconstruction is complex. Moreover, it does not take into account the dynamicity of the SDH/SONET frame.